(1) Field of the Present Invention
The present invention relates to a backlight source and, more particularly, to a backlight source with at least two kinds of electroluminescence devices.
(2) Description of the Prior Art
Following the advancement of the display technique, the liquid crystal display (LCD) is widely applied to substitute for traditional CRT monitor. The LCD is very popular by the consumer, since its light weight, small volume, and low-radiation. The LCD has been regarded as the mainstream product at present, and widely applied to many electronic products, such as computer, personal digital assistant (PDA), laptop, digital camera, and mobile phone.
Because the LCD is a non-self-luminous display device, the LCD cannot provide bright image actively. Thus, the LCD needs a backlight module to provide illumination of the image. Generally speaking, the luminous character of the backlight source is highly bright and uniform. Furthermore, the light emitting angle of the backlight module affects the usage efficiency of light and the angle of view directly. Therefore, the development of the backlight module technique is an important factor to develop LCD in the future.
The conventional backlight module uses the cold cathode fluorescent lamp (CCFL) as the backlight source. Because of the environmental consciousness raising in recent years, the CCFL with mercury is gradually substituted with the LED due to the characteristics of power saving, environmental protection, small volume, high color purity, good reliability, and long life.
Because of the rapid development of the LED, the luminous efficiency is greatly promoted. The high color purity of the LED substantially improves the vividness, chroma, and tone of color, and increases the range of color, thereby to achieve better color performance.
The LED used in the conventional direct type backlight module is Lambertian luminescence type or so-called upward light type. Referring to FIG. 1A, which illustrates the optical field distribution of the luminescence type of a single upward light type. The luminescence type is radial type, and the luminescence type is similar to the Lambertian model of the Lambertian luminescence type.
For the directly type of a backlight module, the backlight source has a backlight source cavity 2, a plurality of LEDs 1 disposed inside the backlight source cavity 2, and a diffuser plate 4 disposed above the backlight source cavity 2.
Referring to FIG. 1B, which illustrates a part view of a conventional backlight source. The arrangement configuration of the LEDs 1 inside the backlight source cavity 2 is an array type and each LED has a light type is the same each other.
Referring to FIG. 1C, which illustrates the luminous intensity distribution of a section a-a′ in FIG. 1B. Due to the influence of the luminescence type, angle of light type, brightness, and the arrangement spacing of the LEDs 1, and when the overall thickness of backlight module being reduced, the brightness uniformity of the backlight module is then decreased and appear a staggered dark band. The dark band is the region of a concave wave shape in FIG. 1C. The dark band phenomenon lowers the quality of the image.
Therefore, under the trend of the tiny and high quality LCD, how to improve the brightness uniformity of the backlight module is an important task.